Production of olefinic c5 hydrocarbons



Oct. 7, 1958 R. A.- FINDLAY PRODUCTION oF oLEFINrc c5 HmRocARBoNs Filed March 2s, 195e United States Patent O PRODUCTION F OLEFINIC C5 HYDROCARBONS Robert A. Findlay, Bartlesville, Okla., assignor to Phillips Petroleum Company, acorporation of Delaware Application March 28, 1956, Serial No. 574,495

10 Claims. (Cl. 260-683.3)

This invention relates to the production of high octane fuels. In one aspect, this invention relates to the dehydrogenation of saturated C hydrocarbons to produce olenic C5 hydrocarbons having increased octane numberms. In another aspect, this invention relates to the production of olenic hydrocarbons by the dehydrogenation of saturated C5 hydrocarbons, which olefnic hydrocarbons can be used in the blending of high octane fuels or further processed for the production of high octane fuels.

One source of blending stocks for the production of fuels for internal combustion engines, both automotive and aviation, has been the comparatively large supply of the normally liquid hydrocarbons, such as pentanes, isopentanes, etc. However, the amount of said hydrocarbons which can be blended into finished fuels is limited by the relatively low octane number and high volatility of said normally liquid hydrocarbons. In recent years, due to advances in the design of internal combustion engines, there has been an ever increasing demand for higher octane number fuels which has further decreased the amount of these hydrocarbons which can be so used. This has led to the development of processes such as dehydrogenation, isomerization, catalytic reforming, etc. for converting said normally liquid hydrocarbons into other hydrocarbons having increased octane numbers. In some instances, special fractions or cuts have been processed.

The demand for ever increasing octane numbers has created a demand for super fuels, i. e., fuels having extraordinarily high blending octane numbers which can be used to blend with the lower octane number materials. It has been known that normal pentane and isopentane, having octane numbers of 58 and 91 respectively (research method) can be dehydrogenated to give. oleiinic C5 hydrocarbons, for example, Z-pentene and 2methyl2 butene, having blending octane numbers within the range of 120 to 150, depending upon the material with which they are blended. The problem in the production of such fuels has been primarily two-fold: (l) separation of the desired olenic hydrocarbons from the reaction product including other oleinic hydrocarbons and the unreacted saturated hydrocarbon; and (2) increasing the yield of the desired olefnic hydrocarbon.

I` have discovered a combination of processing steps which provides for both a more efficient recovery of the desired olefinic C5 hydrocarbons, and an increased yield of said desired olenic C5 hydrocarbons, for example, the 2pentenes and 2'methyl2butene, from the reaction effluent of a saturated C5 hydrocarbon dehydrogenation process. Herein and' in the claims, unless otherwise specified, the term 2pentene' isused to refer. to and include both the cisand transforms of Z-pentene.

An object of this inventionis to. provide. an improved method for the production of olenic C5 hydrocarbons from saturated C5 hydrocarbons. Another object of this invention is to provide an improved method for separatlng desired olenic C5 hydrocarbons, such as 2-pentene and Z-methyl-Z-butene, from the reaction effluent of a saturated C5 hydrocarbon dehydrogenation process. Still another object of this invention is to increase the production of desired olefinic C5 hydrocarbons in a saturated C5 hydrocarbon dehydrogenation process. A still further object of this invention is to provide an improved process for converting relatively high volatility, relatively low octane number, saturated C5 hydrocarbons into olenic C5 hydrocarbons having relatively low volatility and higher octane numbers. Other aspects, objects and advantages of the invention will be apparent to those skilled in the art upon study of this disclosure.

Thus, according to the invention there is provided a method comprising a combination of steps for producing a high octane fuel from a saturated C5 hydrocarbon. Said saturated C5 hydrocarbon is dehydrogenated in the presence of a suitable catalyst. Reactor ellluent is deethanized and is then fractionated in a rst fractionation step to obtain a first overhead fraction comprising paraffmic and olenic C3 to C5 hydrocarbons lower boiling than isopentane, and a first bottoms fraction comprising isopentane, and parafluic and olenic C5 hydrocarbons higher boiling than isopentane. Said iirst bottoms fraction is then fractionated in a second fractionation step to give a second overhead fraction comprising isopentane and 'olefinio C5 hydrocarbons lower boiling than normal pentane, and a second bottoms fraction comprising normal pentane and C5 olenic hydrocarbons higher boiling than normal pentane. Said second bottoms fraction is then solvent extracted with a suitable selective solvent to obtain a raffinate comprising normal pentane which is recycled to said dehydrogenation step, and an extract comprising said C5 olenic hydrocarbons higher boiling than normal pentane, as a product of the process.

In one embodiment of the invention, the overhead from the first fractionation step, i. e., the parairinic and olenic C3 to C5 hydrocarbons lower boiling than isopentane, is removed and charged to an alkylationl unit Iwherein the olenic hydrocarbons are used to alkylate an isoparaflin, such as isobutane, and saturatedv C5 hydro-v carbons produced inl said alkylation processl are recycled asa part of the feed to the dehydrogenation step.

In another embodiment of the invention, at least' a portion of the overhead from the second fractionation step, i.. e., isopentane and oleiinic' C5 hydrocarbons lower boiling than. normalk pentane, is charged to an alkylation unit wherein saidk unsaturated hydro-carbons are used to' allcylate an. isoparaiin, such as isobutane, and' saturated C5 hydrocarbonsV producedL in the alkylation process are recycled as a part of the feed to thef dehydrogenation step. Said alkylation unit can be the sameV to which the overhead from the first fractionation step is charged or a different alkylation unit; Since the o'lens in the overhead1y stream fromthe second fractionation zone are' predominately C5 olens it will be advantageous inl someinstances t'o provide4 separate: alkylation because the alkylate produced from C4- oleiins has a higher octane number than that produced. from C5 olefins.

It is: to be noted. that. iny all' embodiments of theV invention, the overheadv stream from the rst fractionation: step is removed and isnot returned to the dehydrogenation step. A `conventional method of operation would be to perform only one fractionation step andretur-n all the overhead stream therefrom, comprising isopentene and lower boiling hydrocarbons, to the dehydrogenation zone. By providing two fractionation steps I decrease the amount of olens which are recycled to the dehydrogenation zone. In catalytic dehydrogenation processes, the dehydrogenation reaction tends to approach an equilibrium and the presence of excess oleiins in the reaction zone will-prevent the reaction from proceeding as far toward completion as it normally would in the absence of said olens. Therefore, by removing said overhead stream from the first fractionation step and not returning it Vto the dehydrogenation zone I avoid the presence of excess oleins in the dehydrogenation zone and obtain a higher conversion per pass of the paran hydrocarbons to oletins.

A further advantage of my improved process is that by combining an alkylation step with the dehydrogenation step, the lower boiling olenic hydrocarbons and the undesired olefinic hydrocarbons removed overhead from the first and second fractionation steps can be etiiciently utilized to produce alkylate having a relatively high octane number and a relatively low volatility. Said alkylate is an excellent blending stock for the produc-tion of high octane fuels. A further advantage of my combination of a dehydrogenation step and an alkylation step is that the saturated C5 hydrocarbons produced in the alkylation step can be dehydrogenated in the dehydrogenation step. Thus, each unit produces feed stock for the other u nit. This is real and effective cooperation between theunits of the combination.

It is within the scope of the invention to dehydrogenate normal pentane and isopentane separately, or in admixture.

The drawing is a diagrammatic flow sheet illustrating the several embodiments of the invention.

Referring now to the drawing, the invention will be more fully explained. A mixture of pentanes containing about 40 percent isopentane and about 60 percent normal pentane is charged through line into dehydrogenation Zone 14. Pentanes from line 11, isopentane plus C5 olelins from line 13, and a hydrogen rich gas from line 12, all from sources hereinafter described, are mixed with said lmixture of pentanes in line 10 and also charged to dehydrogenation zone 14. Said dehydrogenation zone 14 can be either a fixed bed type or of the fluidized bed type. It is also to be understood that while shown in the drawing diagrammatically, dehydrogenation zone 14 includes such conventional equipment as a heating fur* nace and suitable separation equipment not shown in the drawing. Gaseous efuent from said dehydrogenation zone is passed through line 16 and compressor 17, wherein it is compressed to about 50-150 p. s. i. g., and introduced into absorber zone 18 wherein it is contacted lcountercurrently with a suitable lean absorbent such as mineral seal oil introduced through line 19. Said absorber 18 functions primarily as a deethanizer, i. e., normally gaseous hydrocarbons lower boiling than propane, and hydrogen are removed from the top thereof through line 21. A portion of said gases can be recycled to the dehydrogenation zone via line 22, compressor 23, line 12 and line 10 as previously mentioned. Excess gases can be removed through line 24. Rich absorbent is removed from the bottom of absorber Zone 18 through line 26 and introduced into stripping zone 27. Lean absorbent is recycled from stripping zone 27 via line 19 to said absorber zone 18. Deethanized eluent is passed via line 28 into first fractionation Zone 29 from which there is Vremoved overhead through line 30 a rst overhead fraction comprising parainic and oletinic C3 to C5 hydrocarbons lower Iboiling than isopentane. A first bottom-s fraction is removed through line 31 and comprises isopentane, and paraiinic and olefinic C5 hydrocarbons higher boiling than isopentane. Said rst bottoms fraction is introduced into a second fractionation zone 32 from which there is removed a second overhead fraction 4 via line 33 comprising isopentane and olenie C5 hydrocarbons lower boiling than normal pentane.

A second bottoms fraction, comprising norman pentane and C5 olefinic hydrocarbons higher boiling than normal pentane, is removed from fractionation zone 32 via line 34 and introduced into solvent extraction zone 36 wherein it is contacted countercurrently with a suitable selective solvent introduced through line 37. Normal pentane and other saturated hydrocarbons are removed overhead as a railinate phase from zone 36 via line 38, passed through water washing zone 39 for the removal of solvent, and returned via lines 40 and 13 to dehydrogenation zone 14. Olenic hydrocarbons, primarily Z-pentene and 2-methyl2butene are removed from zone 36 via line 42 as extract phase and introduced into solvent recovery still 45. Solvent is removed from said still 45 via line 37 and returned to said extraction zone 36. Said Z-pentene and Z-methyl-Z-butene, are recovered from said still 45 and removed via line 43 to storage 44 as product of the process.

In one embodiment of the invention, the overhead stream in line 3G from the first fractionation zone 29 is introduced into alkylation zone 46. Isoparatiin, such as isobutane, is introduced through line 50 into said alkylation zone. Butenes from other sources (such as refinery cracking operations) can also be added to alkylation zone 46 through a line not shown. Said hydrocarbons are contacted and admixed in the presence of a suitable alkylation catalyst such asV hydrofluoric acid and said isoparaftin is alkylated by `said oletins. Alkylation zone effluent is passed via line 47 into fractionation zone 48 wherein it can be fractionated according to any desired separation. The separation shown in the drawing is one most usually eected. 'Saturated C5 hydrocarbons in the alkylation zone eftluent are recycled via line 11 to dehydrogenation zone 14. Isobutane is recycled via line 49 to alkylation zone 46. If it is not desired to alkylatc the overhead stream in line 30 said 'stream can be withdrawn via line 25 for other use.

`In another embodiment of the invention, a portion of the overhead stream from the second fractionation zone 32 can be passed via lines 33 and 35 into said alkylation zone 46. The amount of said second overhead stream passed to said alkylation zo-ne is determined largely by the concentrations of oletins in said overhead stream. It is desirable to prevent buildup of a large olefin recycle so as to suppress diolefin formation and to favor the primary dehydrogenation reaction. The oleiins in this stream are alkylated in the manner previously described. It is within the scope of the invention to alkylate the overhead streams from said rst fractionation Zone and from said second fractionation zone either separately or together.

Any suitable dehydrogenation catalyst can be employed in the dehydrogenation step of the invention. A presently preferred catalyst is an unsupported chromium `oxide gel catalyst. Said catalyst can be employed in either pelleted or granular form, or in finely divided form. One advantageous way of preparing said catalyst is as follows. Acetic acid is added to a l0 percent aqueous solution of chromic nitrate until the solution contains 20 percent of acid. Ammonia is then added until in slight excess. The precipitated gel is removed from the supernatant liquid, washed thoroughly with water and slowly dried. The dried gel is dark colored, translucent and vitreous, and possesses a highly developed gel structure which is retained when the gel is heated in use as a catalyst. Further details regarding the preparation of said catalyst can be found in Patent 1,905 ,383, issued April 25, 1932, to Huppke et al.

The chromium oxide gel catalyst is preferred because it permits operation of the dehydrogenation step at a lower temperature than most other catalysts. It is desirable to carry out the dehydrogenation step at the lowest possible temperature for several reasons. (l) To decrease the decomposition of the C5 hydrocarbons to lower paraffin hydrocarbons. (2) To suppress the formation of dioleiins which are undesirable because they tend to form gum in motor fuel and also to cause higher acid consumption in the alkylation step. (3) To favor the for- 5 mation of 2-olens rather than the formation of l-oleins (at the lower temperatures, the equilibrium favors isomerization of the double bond toward the middle of the molecule). Other dehydrogenation catalysts which can be used include a 40 percent chromia-10 percent beryllia-SO percent alumina catalyst prepared as disclosed and claimed in Patent 2,483,929, issued October 4, 1949, to J. R. Owen; and a 20 percent chromia-SO percent alumina catalyst disclosed and claimed inv Patent 2,606,159, issued August 5, 1952, to I. R. Owen; and other catalysts disclosed and claimed in said patents.

The dehydrogenation stepy can be carried out at temperatures ranging from 900 to 1150 F. However, in order to achieve the above advantages of low temperature operation, it is preferred to carry out said dehydrogenation step at temperatures within the range of 900 to 1000 F., more preferably at temperatures between 925 and 960 F.

As might be expected from thelaw of mass action, the dehydrogenation reaction is favored by low absolute or partial pressures. Low absolute pressures, i. e., below atmospheric pressure, while favorable to the dehydrogenation reaction are generally undesirable in commercial operations due to the diculty of preventing leakage of air into the system. For this reason, it is customary to employ pressures somewhat above atmospheric, i. e., within the range of 0 to 50 p. s. i. g., preferably 0 to. 30 p. s. i. g., and more preferably within the range of 0 to 15 p'. s. i. g.

The space velocity in the dehydrogenation step will usually be in the range of 800 to 1600 gaseous volumes per volume of catalyst per hour. It is preferred to carry out the dehydrogenation reaction in the presence of hydrogen present in an amount of about 1 mol per mol of feed stock so as to suppress the formation of dioleiins 40 ratio within the range of 10 to 20:'1, preferably 12 to 15:1. The solvent extraction tower is usually operated at temperatures of about 100 F. and under sufficient pressure to maintain the hydrocarbons in liquid phase, e. g. about 25 p. s. i. g. Other solvents which can be used include furfural, aqueous phenol, and other glycol ethers similar to methyl Carbitol.

Operating conditions in the alkylation zone are generally as follows: isoparaiiin to olefin ratio, Within the range of 4.5 :1 to 8:1 or higher; temperature 80 to 120 F.; and acid to hydrocarbon ratio about 1:1.

The following example will serve to further illustrate the invention.

' EXAMPLE I A mixture consisting essentially of about 40 percent isopentane and about percent normal pentane is vaporized, mixed with hydrogen in an amount of about l mol of hydrogen per mol of charge stock, and passed through a dehydrogenation reactor containing a fixed bed of chromium oxide gel catalyst prepared as described above. Said catalyst bed is maintained at a temperature-of 935 F. and under a pressure of 10 p. s. i. g. After being compressed and deethanized the e'luent from the reaction zone is fractionated in a rst fractionation step to give a first overhead fraction comprising C3 hydrocarbon, l-butene, Z-butene, butanes, and 3-methyl-1-butene, and a first bottoms fraction comprising isopentane, l-pentene, Z-pentene, 2-methyl-2-butene and normal pentane. Said rst bottoms fraction is then fractionated in a second fractionation step to give a second bottoms fraction comprising normal pentane, Z-pentene, and 2-methyl-2- butene. Said second bottoms fraction is then solvent extracted with 14 volumes of methyl Carbitol solvent containing l0 percent water to yield a raffinate comprising normal pentane, and an extract comprising Z-pentene and 2-methyl-2-butene. Said extract isobtained in a yield of 70.3 mol percent based on the fresh charge to the dehydrogenation step.

Table I below sets forth a material balance for this example.

Table L Material balance Dehydro.

Fraction- Fraction- Fractionator No. ator No. ator N o. Ranate, Extract Boiling Point,

1,bot 2, Over- 2, Bot- Mols (Prod- F. toms, head, toms, uct), Mols Mols Mols ols Com- Fraction- Fresh Recycle bined Zone ator No. Charge, Stream, Feed, Effllu- 1, Over- Mols Mols Mols ent 1, ead, Mols ols C!3 (Propane, Propylene). 0. 3 Butenes 0. 5 Butanes 0.5 3-Methyl-butene-1.- 0. 8 Isopentane 8. 4 32. 8 41. 2 33. 1 l-Pentene 3. 3 3. 3 3. 3 2-Methyl1butene 2. 8 2. 8 2. 8 Normal Pentane 12. 5 41. 5 54.0 41. 9 2-Pentene 0. 2 0. 2 7; 4

2Methy12-butene 0.2 0.2 7. 7 C5 Dioletns 0. 3 0 3 1. 8 Total-Mols 81. 1 102. 0 100. 0

97.3 Cis, 98.4

Trans.

l 2.0 mols gas (C2 and lighter) removed in absorber after dehydrogenation.

and to extend the life of the catalyst. Too much hydrogen should be avoided because the presence of excess hydrogen is unfavorable to the dehydrogenation reaction.

Operating conditions in the two fractionation steps of the invention will depend upon the composition of feed to the fractionation zones and the degree of separation which it is desired to effect as will be understood by those skilled in the art.

Any suitable selective solvent can be employed for the solvent extraction of the bottoms fraction from the second fractionation step, i. e., the separation of the normal pentane from the desired oleiinic C5 hydrocarbons. A presently preferred solvent i's methyl Carbitol (diethylene glycol monomethyl ether) containing from 5 to 25 percent water, preferably 10 to 15 percent water. Said ,solvent is usually employed in a solvent to hydrocarbon The extract product of the invention (see Example I and Table I above), comprising Z-pentenes and 2-methyl- Z-butene has an especially high blending octane number. When said product is blended with a platformate (obtained by catalytically reforming a straight-run gasoline, obtained from a mixture of West Texas and Gulf Coast crude oils, in the presen-ce of a platinum-containing catalyst) in amounts of as low as only 10 percent by volume, there is a marked increase in the octane number. Table II given below shows tests on (l) said platformate, (2') a blend containing volume percent of said platformate and 10 volume percent of mixed pentanes (the charge stock for Example I), and (3) a `blend containing 90 volume percent of said platformate and 10 volume percent. of the high octane fuel product of Example I.

Table Il Blenang A comparison of the data given above in Table II shows that the original mixed pentanes actually lower the octane number of the platformate when blended therewith; whereas, the high octane fuel product of the invention increases the octane number of said platfonnate by more than three numbers, showing that the blending octane number of said high-octane fuel product is about 123 in this instance. It is also to be noted that the Reid vapor pressure of the blend containing the high-octane fuel product of the invention is considerably lower than the Reid vapor pressure of the blend containing the mixed pentanes. The lower vapor pressure of the blend containing the high-octane fuel of the invention is an important advantage lbecause more butane, or other desirable blending stocks having a high vapor pressure, can be blended into the final motor fuel. This not only makes it possible to produce more motor fuel but also operates to conserve natural resources such as normally gaseous hydrocarbons like butane, etc.

As will be evident to those skilled in the art, various modifications of the invention can be made, in view of the above disclosure, without departing from the scope of said invention.

I claim:

1. A process for the production of unsaturated C hydrocarbons having increased anti-knock value from saturated C5 hydrocarbons, which process comprises the combination of steps; contacting said saturated C5 hydrocarbons with a dehydrogenation catalyst in a dehydrogenation zone to produce a mixture containing parainic and olefinic hydrocarbons; fractionating said mixture in a rst fractionation zone to obtain a first overhead fraction comprising paraflinic and olefinic C5 to C5 hydrocarbons lower boiling than isopentane, and a first bottoms fraction comprising isopentane and parainic and olefinic C5 hydrocarbons higher boiling than isopentane; fractionating said first bottoms fraction in a second fractionation Zone to obtain a second overhead fraction comprising iso-pentane and olefinic C5 hydrocarbons lower boiling than normal pentane, and a second bottoms fraction comprising normal pentane and olefinic C5 hydrocarbons boiling higher than normal pentane; returning at least a portion of said second overhead stream to said dehydrogenation Zone; solvent extracting said second bottoms fraction with a selective solvent to produce a raffinate comprising normal pentane and an extract comprising said C5 oleiinic hydrocarbons higher boiling than norm-a1 pentane; returning said raffinate to said dehydrogenation Zone; and recovering said extract as product of the process.

2. A process according to claim l which comprises, in further combination, the steps of: passing said first overhead fraction to an alkylation Zone; passing an isoparain to said alkylation zone; alkylating said isoparaflin with the olefins in said first overhead fraction in the presence of an alkylation catalyst under alkylation conditions; recovering unreacted isoparaiin from the efuent from said alkylation zone and returning same to said alkylation zone; recovering substantially saturated C5 hydrocarbons from said alkylation zone eiuent; and returning said C5 hydrocarbons to said dehydrogenation Zone as a portion of the charge stock thereto.

3. `A process according to claim l which comprises, in further combination, the steps of: passing at least a portion of said second overhead fraction to an alkylation zone; passing an isoparaflin to said alkylation zone; alkylating said isoparain with the olens in said second overhead fraction in the presence of an alkylation catalyst under alkylation conditions; recovering unreacted isoparalin from the etiiuent from said alkylation zone and returning same to said alkylation zone; and recovering substantially saturated C5 hydrocarbons from said alkylation zone eluent and returning said C5 hydrocarbons to said dehydrogenation zone as a portion of the charge thereto.

4. A process according to claim 2 wherein at least a portion of said second fractionation zone overhead is passed to said alkylation zone.

5. The process of claim 2 wherein said isoparaffin is isobutane and said alkylation catalyst is hydrofluoric acid.

6. A process for the production of 2-pentene and 2- methyl-Z-butene from a mixture of normal pentane and isopentane, which process comprises the combination of steps: contacting said mixture with a dehydrogenation catalyst in a dehydrogenation zone to produce a dehydrogenation zone efiluent containing parainic and olenic hydrocarbons; fractionating said eilluent in a first fractionation zone to obtain a first overhead fraction comprising l-butene, Z-butene, butanes, and 3-methyl-1- butene, and a rst bottoms fraction comprising isopentane, l-pentene, Z-methyl-l-butene, normal pentane, 2- pentene, and Z-methyl-Z-butene; fractionating said first bottoms fraction in a second fractionation zone to obtain a second overhead fraction comprising isopentane, l-pentene, and 2-methyl-1-butene, and a second bottoms fraction comprising normal pentane, 2-pentene, and 2- methyl-Z-butene; returning at least a portion of said second overhead fraction to said dehydrogenation zone; solvent extracting said second bottoms fraction with a selective solvent and recovering a raiiinate comprising normal pentane, and an extract comprising Z-pentene and Z-methyl-Z-butene; returning said ratiinate to said dehydrogenation zone; and recovering said extract as a product of the process.

7. A process according to claim 6 which comprises, in further combination, the steps of: passing said rst overhead fraction to an alkylation zone; passing isobutane to said alkylation zone; alkylating said isobutane with the olens in said lirst overhead fraction in the presence of hydrouoric acid alkylation catalyst under alkylation conditions; recovering unreacted isobutane from the effluent from said alkylation zone and returning same to said alkylation zone; recovering substantially saturated C5 hydrocarbons from said alkylation zone effluent; and returning said C5 hydrocarbons to said dehydrogenation Zone as a portion of the charge stock thereto.

8. A process according to claim 6 which comprises, in further combination, the steps of: passing at least a portion of said second overhead fraction to an alkylation zone; passing isobutane to said alkylation zone; alkylating said isobutane with the olefins in said first overhead fraction in the presence of hydrofluoric acid alkylation catalyst under alkylation conditions; recovering unreacted isobutane from the effluent from said alkylation zone and returning same to said alkylation zone; recovering substantially saturated C5 hydrocarbons from said alkylation zone eiuent; and returning said C5 hydrocarbons to said dehydrogenation zone as a portion of the charge stock thereto.

9. A process according to claim 7 wherein at least a portion of said second fractionation zone overhead is passed to said alkylation zone.

10. A process according to claim 7 wherein said dehydrogenation catalyst is a chromium oxide gel catalyst; said dehydrogenation zone is operated at a temperature within the range of 900 to 1000 F., a pressure within the range of 0 to 30 p. s. i. g.; and said selective solvent is dethylene glycol monomethyl ether containing from 10 to 15 percent by volume of water.

References Cited in the le of this patent UNITED STATES PATENTS Huppke et a1. Apr. 25, 1933 Morrell et a1. Feb. 21, 1939 Duncan et a1. June 17, 1941 Frey Sept. 28, 1948 

1. A PROCESS FOR THE PRODUCTION OF UNSATURATED C5 HYDROCARBONS HAVING INCREASED ANTI-KNOCK VALUE FROM SATURATED C5 HYDROCARBONS, WHICH PROCESS COMPRISES THE COMBINATION OF STEPS; COMTACTING SAID SATURATED C5 HYDROCARBONS WITH A DEHYDROGENATION CATALYST IN A DEHYDROGENATION ZONE TO PRODUCE A MIXTURE CONTAINING PARAFFINIC AND OLEFINIC HYDROCARBONS; FRACTIONATING SAID MIXTURE IN A FIRST FRACTIONATION ZONE TO OBTAIN A FIRST OVERHEAD FRACTION COMPRISING PARAFFINICA AND OLEFINIC C3 TO C5 HYDROCARBONS LOWER BOILING THAN ISOPENTANE, AND A FIRST BOTTOMS FRACTION COMPRISING ISOPENTANE AND PARAFFINIC AND OLEFINIC AC5 HYDROCARBONS HIGHER BOILING THAN ISOPENTANE; FRACTIONATING SAID FIRST BOTTOMS FRACTION IN A SECOND FRACTIONATION ZONE TO OBTAIN A SECOND OVERHEAD FRACTION COMPRISING ISO-PENTANE AND OLEFINIC C5 HYDROCARBONS LOWER BOILING THAN NORMAL PENTANE, AND A SECOND BOTTOMS FRACTION COMPRISING NORMAL PENTANE AND OLEFINIC C5 HYDROCARBONS BOILING HIGHER THAN NORMAL PENTANE; RETURNING AT LEAST A PORTION OF SAID SECOND OVERHEAD STREAM TO SAID DEHYDROGENATION ZONE; SOLVENT EXTRACTING AID SECOND BOTTOMS FRACTION WITH A SELECTIVE SOLVENT TO PRODUCE A RAFFINATE COMPRISING NORMAL PENTANE AND AN EXTRACT COMPRISING SAID C5 OLEFINIC HYDROCARBONS HIGHER BOILING THAN NORMAL PENTANE; RETURNING SAID RAFFINATE TO SAID DEHYDROGENATION ZONE; AND RECOVERING SAID EXTRACT AS PRODUCT OF THE PROCESS. 